The European Food Safety Authority dismissed a study linking a Monsanto weedkiller to cancer after counsel from a US Environmental Protection Agency officer allegedly linked to the company.

Jess Rowlands, the former head of the EPA’s cancer assessment review committee (CARC), who figures in more than 20 lawsuits and had previously told Monsanto he would try to block a US government inquiry into the issue, according to court documents.

The core ingredient of Monsanto’s RoundUp brand is a chemical called glyphosate, for which the European commission last week proposed a new 10-year license.

Doubts about its regulatory passage have been stirred by unsealed documents in an ongoing US lawsuit against Monsanto by sufferers of non-hodgkins lymphoma, who claim they contracted the illness from exposure to RoundUp.

“If I can kill this, I should get a medal,” Rowlands allegedly told a Monsanto official, Dan Jenkins, in an email about a US government inquiry into glyphosate in April 2015.

In a separate internal email of that time, Jenkins, a regulatory affairs manager, said that Rowlands was about to retire and “could be useful as we move forward with [the] ongoing glyphosate defense”.

Documents seen by the Guardian show that Rowlands took part in a teleconference with Efsa as an observer in September 2015.

Six weeks later, Efsa adopted an argument Rowlands had used to reject a key 2001 study which found a causal link between exposure to glyphosate and increased tumour incidence in mice.

Rowlands’ intervention was revealed in a letter sent by the head of Efsa’s pesticides unit, Jose Tarazona, to Peter Clausing, an industry toxicologist turned green campaigner.

In the missive, Tarazona said that “the observer from the US-EPA [Rowlands] informed participants during the teleconference about potential flaws in the Kumar (2001) study related to viral infections.”

Efsa’s subsequent report said that the Kumar study “was reconsidered during the second experts’ teleconference as not acceptable due to viral infections”.

Greenpeace said that news of an Efsa-Rowlands connection made a public inquiry vital. “Any meddling by Monsanto in regulatory safety assessments would be wholly unacceptable,” said spokeswoman Franziska Achterberg. “We urgently need a thorough investigation into the Efsa assessment before glyphosate can be considered for re-approval in Europe.”

A reply to Tarazona’s letter from Clausing, seen by the Guardian, also says: “In the light of Jess Rowland’s role in the assessment of carcinogenicity of glyphosate in the US as reflected by the internal Monsanto documents, I have serious concerns that he might have influenced the decision by providing wrong information which has not been scrutinised by Efsa and its experts.”

A Monsanto spokesman said: “Plucking a single email out of context doesn’t change the fact that the US EPA and regulators around the world, as well as a branch of the World Health Organization (WHO) that analysed pesticide residues, have concluded that glyphosate is unlikely to pose a carcinogenic risk to humans.”

Tarazona declined to comment on Rowlands’ contribution to the Efsa study but said that Kumar’s paper had been compromised by the use of Swiss albino mice.

“The issue of ‘high background incidence’ is something common to all studies that use that strain of mouse,” he said. “There was [also] the fact that the effect was observed only at a very high dose level.”

Other toxicologists, such as Prof Ivan Rusyn, who contributed to a WHO assessment of glyphosate, contend that where sample sizes are limited, “the most informative animal studies are those conducted with sufficiently high doses”.

Clausing said that there was “almost no difference” between malignant lymphomas in Kumar’s control group, compared to others.